As optical data processing circuits approach multigigahertz operation rates, the need arises for high-speed optical interconnects for signal transmission and routing. This requires high-speed electro-optic modulators and switches that convert the electronic signal to optical. The electronic circuits that drive the electro-optic modulators and switches provide low voltage levels at high speeds. This dictates the performance goals required for the electro-optic modulators and switches. Currently employed electro-optic modulators and switches have drive voltages much too large for high-speed operation.
Electro-optic modulation or switching is represented generally in the top view drawing of FIGS. 1a and 1b. As the basic form of an electro-optic switch, the directional coupler, shown in FIGS. 1a and 1b is known, with FIG. 1a showing a switch without applied drive or modulation or switching voltage and FIG. 1b showing a switch with applied drive or modulation or switching voltage. A directional coupling type of electro-optic switch is one that controls the transfer of the optical signal by causing the, index of refraction of the switch""s coupling portion to change by an electro-optic effect. The FIG. 1a top view illustrates a switch having wave guides etched from a wafer including a layer of non-linear electro-optic polymer material.
Parallel channel wave guides separated by a finite distance for receiving one or more optical signals are represented in both FIGS. 1a and 1b at 101, 102 and 112 and 113, respectively. A single optical input signal is considered for purposes of the present discussion and is represented by the bold arc at 103 and 114 in FIGS. 1a and 1b, respectively. A symmetric mode of the optical signal, as represented at 105, and an antisymmetric mode of the optical signal as represented at 104 in FIG. 1a and at 116 and 115 in FIG. 1b, respectively, are generated upon entering the switch and these modes travel along the length of the channel or switch, over such lengths as are represented at 106 and 121 in FIGS. 1a and 1b respectively. The phase of the two modes shift as the respective signals travel the length of the wave guides, as is represented in the dotted, curved lines, shown at 108 In FIG. 1a and at 119 in FIG. 1b and the solid, curving lines shown at 107 and 120 in FIGS. 1a and 1b, respectively. The symmetric mode is the mode of propagation within the other wave guide region. With no voltage applied to the FIG. 1 switches, complete transfer of light from one channel to the next occurs at a distance that introduces a voltage independent xcfx80/2 phase shift to the modes so that the one mode couples completely to the other. Complete mode coupling and light transfer occurs at the output wave guides at 126 in FIG. 1a and thereafter the complete optical signal at 111 exits the wave guide at 128 in FIG. 1a. 
Applying an electric field to one of the channels of the directional coupler of FIG. 1b over the distance L represented at 121 from the voltage source shown at 122 in FIG. 1b will alter the dielectric properties of the coupler""s non-linear polymer material subjected to the electric field, hence changing the index of refraction of the material and introducing a voltage dependent xcfx80/2 phase shift in the signal modes 115 and 116 and thereby modulation or switching the wave guide from 129 to 130 through which the signal exits as represented at 125 in FIG. 1b. 
Past research has focused on exploiting the electro-optic properties of non-linear electro-optic polymers with optimized optical, structural and mechanical properties to achieve high performance electro-optic devices, such as modulators and switches. Non-linear electro-optic polymers have several attractive potential characteristics that many researchers have tried to capitalize on over the past decade. These include a high non-linearity or electro-optic coefficient enabling potential low voltage operation. a low dielectric constant for high speed modulation, low temperature processing enabling integration of optics with electronics, excellent refractive index match with optical fiber materials and simplified fabrication for lower cost.
Several technical barriers have heretofore prevented the use of non-linear electro-optic polymers from progressing toward commercialization thus far. Breakthroughs in the development of non-linear electro-optic polymers over the last couple of years have demonstrated 100+pm/V electro-optic coefficients for potential low voltage electro-optic device operation. This has led to a recently reported milestone of less than 1 Volt operation voltage. However, even though device modulation and modulation or switching voltages have been dramatically reduced by utilizing these new materials, the resulting modulation or switching voltages are still much higher than required for high speed operation.
In considering modulation and modulation or switching voltages, one must first determine those parameters that affect modulation voltage for electro-optic devices. The voltage necessary to realize the desired xcfx80 phase retardation for a conventional transverse electro-optic modulator is defined as the half wave voltage Vxcfx80 and is given by                                           V            π                    =                                    λ              ⁢                              xe2x80x83                            ⁢              d                                                      n                3                            ⁢                              r                33                            ⁢              l                                      ,                            (        1        )            
where xcex is the wavelength, d is the thickness of the electro-optic material, n is the index of the electro-optic material, r33 is the electro-optic coefficient of the electro-optic material and 1 is the length of the interaction region. For a given geometry, Vxcfx80 will be inversely proportional to the electro-optic coefficient r33. Thus, it is desired to maximize r33 in order to minimize Vxcfx80
Now, the value for r33 is determined by previous application of a large poling field across the active polymer film when heated to near its transition temperature Tg and then allowed to cool to room temperature while keeping the electric field applied. This poling field is chosen to be as large as possible, yet just less than that which would result in dielectric breakdown of the material.
However, practical non-linear electro-optic polymer based electro-optic modulators and switches require polymer cl adding layers in addition to the non-linear electro-optic polymer core in order to confine the optical signal within the core region. The cladding layers control how much poling voltage is dropped across the core region and thus controls the non-linearity or electro-optic coefficient r33. The present invention overcomes the barriers to commercial use of non-linear electro-optic polymers by maximizing the poling efficiency of and in-turn maximizing the electro-optic coefficient of non-linear electro-optic polymer materials making up the core layer within an electro-optic wave guide device structure that includes cladding layers and conductive charge sheet layers. The present invention will render lower operating voltages, shorter device lengths and also reduce optical propagation loss.
The present invention provides a non-linear electro-optic polymer based, integrated optic, electro-optic device utilizing a non-linear electro-optic polymer for the optical wave guide core layer sandwiched between two very thin optically transparent electrically conductive charge sheet poling electrode layers which are, in turn, sandwiched between two optical wave guide cladding layers.
It is an object of the present invention to provide a non-linear electro-optic polymer based, integrated optic, electro-optic device having a maximized electro-optic coefficient.
It is another object of the present invention to provide a non-linear electro-optic polymer based, integrated optic, electro-optic device having minimized device operating voltages.
It is another object of the invention to provide a non-linear electro-optic polymer based, Integrated optic, electro-optic device having maximized realizable device speed.
It is another object of the invention to provide a non-linear electro-optic polymer based, integrated optic, electro-optic device having maximized poling efficiency, which will also render the lowest possible poling voltage, making it possible to pole the devices in-situ within electronic circuits.
It is another object of the invention to provide a non-linear electro-optic polymer based, integrated optic, electro-optic device having extended life and usefulness beyond known devices.
It is another object of the invention to provide a non-linear electro-optic polymer based, integrated optic, electro-optic device having minimized optical propagation loss induced by the drive electrodes.
These and other objects of the invention are achieved by the description, claims and accompanying drawings and by a minimal propagation loss, electro-optic coefficient maximizing electrically controlled polymer-based optical signal modulation and switching device requiring minimal operating voltage comprising:
a first electrically grounded metal layer overlaying said substrate layer and functioning as an electrical ground electrode;
a first electrically passive polymer cladding layer overlaying said first metal layer and including therein an aperture communicating with said grounded metal layer;
a first optically transparent electrically conductive charge sheet layer overlaying said first electrically passive polymer cladding layer, said first optically transparent electrically conductive charge sheet layer including an integral portion extending through said aperture of said first electrically passive polymer cladding layer and making electrical contact with said first electrically grounded metal layer;
an optical signal transmitting non-linear electro-optic polymer core layer having electrically alterable molecular structure and optical refraction properties;
a second optically transparent electrically conductive charge sheet layer overlaying said optical signal transmitting non-linear electro-optic polymer core layer,
said first and second optically transparent electrically conductive charge sheet layers being capable of establishing an electric field region encompassing said optical signal transmitting non-linear electro-optic polymer core layer in said modulation or switching device;
a second electrically passive polymer cladding layer overlaying said second optically transparent electrical conductive charge sheet layer; and
a second metal layer overlaying said second electrically passive polymer cladding layer and interfacing a switch controlling electrical signal voltage source with said second optically transparent electrically conductive charge sheet layer through said second electrically passive polymer cladding layer;
said non-linear electro-optic polymer core layer transmitting an optical signal in a predictably altered path therein upon application of electric field-sustaining voltage between said first and second optically transparent electrically conductive charge sheet layers.